1. Field of the Invention
The present invention relates to an exhaust system for a watercraft, and more particularly to a monitoring and control system for a catalytic exhaust system of a watercraft.
2. Description of Related Art
Personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and carries a rider and possibly one or two passengers. A relatively small hull of the personal watercraft commonly defines a riders' area above an engine compartment. A two-cycle internal combustion engine frequently powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on the underside of the watercraft hull. The jet propulsion unit is located within the tunnel and is driven by a drive shaft. The drive shaft usually extends between the engine and the jet propulsion device, through a wall of the hull tunnel.
An exhaust system of the personal watercraft discharges engine exhaust to the atmosphere either through or close to the body of water in which the watercraft is operating. Although submerged discharge of engine exhaust silences exhaust noise, environmental concerns arise. These concerns are particularly acute in connection with two-cycle engines because engine exhaust from two-cycle engines often contains lubricants and other hydrocarbons.
Such environmental concerns have raised a desire to minimize exhaustion of hydrocarbons and other exhaust byproducts (e.g., carbon monoxide and oxides of nitrogen), and thus reduce pollution of the atmosphere and the body of water in which the watercraft is operated. In response to the increased concerns regarding exhaust emissions, some personal watercraft engines recently have become equipped with a catalyst to convert exhaust byproducts to harmless gases.
Catalysts must operate at a relatively high temperature in order to produce the necessary thermal reaction and burning of the exhaust byproducts. A catalytic device thus desirably operates within a specific range of temperature so as to effectively and efficiently convert engine exhaust into generally harmless gases.
Some prior exhaust systems have employed a cooling jacket about the catalytic device to maintain the catalytic device within the desired temperature range. In some systems, at least a portion of the cooling water also is introduced into the exhaust system to not only further cool and silence the exhaust gases, but also to assist the discharge of exhaust gases. The added water to the exhaust system, however, gives rise to possible damage to the catalyst.